Intermittent wireless connection and disconnects with DD-WRT and Windows 7

If you’re using DD-WRT on your router you may find that certain wireless configurations cause the wireless clients to either be unable to connect or drop connection. This seems to be the most noticeable on Windows 7 systems, but likely happens on other systems as well. Note that I did not observe this at all on a Linux-based system and I’m completely unable to explain why. Perhaps a difference in the wireless stacks between Windows and Linux highlights this issue.

Issues related to this include not being able to connect to the wireless AP, instead receiving a message such as “The access point did not allow the connection” or something similar (Apologies, I don’t have the exact error message.), and losing wireless connection to the network or AP, even though it is still shown in the list of wireless networks.

This appears to be related to the wireless security settings, specifically the settings for security mode and WPA algorithm. See the following screenshot:

Having the security mode set to WPA2 Personal Mixed and the algorithm set to TKIP+AES appears to cause the problem.

According to the DD-WRT help:

WPA2 Mixed
This mode allows for mixing WPA2 and WPA clients. If only some of your clients support WPA2 mode, then you should choose WPA2 Mixed. For maximum interoperability, you should choose WPA2 Mixed/TKIP+AES.

So, according to this, it should work — but it doesn’t seem to work quite as advertised. Instead, this is the recommended setup as long as all your wireless clients support WPA2:

Security mode set to WPA2 Personal and algorithm set to AES only appeared to completely solve the problem.

For the curious, this is DD-WRT v24-sp2 (08/12/10) mega (SVN revision 14929), the current recommended build.